EXPERIMENTAL INTROGRESSION IN NATURAL TETRAPLOID AEGILOPS SPECIES

In respect to the origin of the tetraploid Aegilops species, Zohary and Feldman (1962) postulated a polyphyletic origin by introgression. However, Kihara (1954) did not consider introgression as a mechanism for producing a new genome form.In order to examine whether or not introgression occurs between tetraploid species belonging to the Polyeides section of Aegilops, cytological and morphological analyses were carried out on hybrid progenies of three ross-combinations; Ae. triaristata (CuMt), Ae. variabilis (CuSv), and Ae. biuncialis (CuMb)×Ae. columnaris (CuMc), where the Cu genome was the common buffer genome and Mt, Sv and Mb were known to form 5, 3.5 and 2 bivalents, respectively, with the Mc genome.In the most closely related combination, Ae. triaristata×Ae. columnaris, introgression was confirmed cytologically and morphologically. Also, in the second, intermediately related combination, Ae. variabilis×Ae. columnaris, only introgression between two homologous chromosomes or chromosome segment(s) was observed. However, in the third distinctly related combination, Ae. biuncialis×Ae. columnaris, no introgression took place.These facts suggest that introgression occurs in connection with the relationship between species and that it is one of the factors responsible for the origin of new genomes and variations in the Aegilops tetraploid species.